1. Field of the Invention
The invention relates to a heating system for heating air, especially for heating the interior of a motor vehicle, with at least a first heater, at least a second heater, and at least one flow path between the first heater and the second heater. The invention also relates to a process for influencing air flows in a heating system for heating air, especially for heating the interior of a motor vehicle, with at least one first heater, at least one second heater, and at least one flow path between the first heater and the second heater. Furthermore, the invention relates to an air heater with a burner, a heat exchanger, an air inlet area, an air exit area, a control device and a temperature sensor which is located in the air inlet area, the temperature in the air inlet area being monitored by means of the temperature sensor which is located in the air inlet area. The invention likewise relates to a process for detecting hot air flowing back through an air heater.
2. Description of Related Art
The use of generic heating systems and generic processes known, especially in the motor vehicle art. Such heaters are characterized by the interaction of a first heater—the motor vehicle heater or a combination of the motor vehicle heater and air conditioner—and a second heater, the auxiliary air heater. The motor vehicle heater or the combination of the motor vehicle heater and air conditioner is called the “front box.” The combination of motor vehicle heater and air conditioner is also known as HVAC (Heat, Ventilation. & Air Conditioning). When in the description of the prior art and in the description of the invention a motor vehicle heater is addressed below, combinations of a motor vehicle heater with an air conditioner are also always intended.
FIG. 14 schematically shows the structure of a system of the prior art. A motor vehicle heater 110 with an air inlet 138 (which is not shown in detail) is connected to a mixing chamber 114. Furthermore, there is an auxiliary heater 112 which has an air inlet 136. The auxiliary heater 112 is also connected to the mixing chamber 114. The mixing chamber 114 has several air channels 140 for the emergence of air. Generally, in the mixing chamber 114, it is possible to reroute the volumetric flow entering there via flaps into the different air channels 140 or to close the air channels 140. In this way, the user is able to undertake various settings for climate control of the interior of the motor vehicle.
In normal operation of the heating system shown in FIG. 14, an air flow 142 emerges from the motor vehicle heater 110 and enters the mixing chamber 114. Likewise, an air flow 144 emerges from the auxiliary heater 112 and enters the mixing chamber 114. As a result of these air flows 142, 144, which are inherently independent of one another, counter-coupling can result which can lead, for example, to a counterpressure 146 against the flow 144 of the auxiliary heater 112. In FIG. 14, the counterpressure 146 is a small amount so that proper operation of the heating system is possible.
FIG. 15 shows a system with a structure which corresponds to that from FIG. 14. In contrast to the operating state which is shown schematically in FIG. 14, the heating system as shown in FIG. 15 does not work properly. This results from the increased counterpressure 146 which, in this case, is so great that it causes a reversal of the air flow 144.
The formation of the operating states shown in FIG. 14 and in FIG. 15 and the resulting problems are explained below.
The motor vehicle heater has a fan which blows air into the mixing chamber with a high volumetric flow and relatively low pressure stiffness. The term pressure stiffness is defined as the potential of a pressure build-up. A high pressure stiffness stands, for example, for the potential to apply a high pressure. The fan of the motor vehicle heater can be controlled continuously or in stages, and this control can be undertaken especially independently of the thermodynamic states in the heating system.
In addition, the auxiliary heater has a fan. The latter, in contrast to the fan of the motor vehicle heater, is relatively pressure-stiff, but with a smaller volumetric flow being produced. In current auxiliary heaters, the fan of the auxiliary heater, in principle, cannot be controlled independently of the heat output of the auxiliary heater. When more heat output is required, the volumetric flow is also increases and vice versa. Based on the change of the volumetric flow of the auxiliary heater, however, the pressure stiffness also changes. The blow-out temperature on the auxiliary heater is dependent, among others, on the resistances opposing the auxiliary heater. For a high resistance, this can lead to an elevated blow-out temperature which is limited by adjusting the auxiliary heater down or turning it off.
Therefore, for operation of the auxiliary heater, it is ideal if it can run at low outside temperatures, with high heat outputs, i.e., high volumetric flows, and thus, high pressure stiffness. The auxiliary heater can then react to the fan of the motor vehicle heater, especially when the latter is operated at low fan stages or if only a few flaps in the mixing chamber are closed.
The problem arises when the auxiliary heater must reduce the heat output as a result of rising temperatures. Based on the above described regularities, then the pressure stiffness, and moreover, the possibility of adequately reacting to the motor vehicle fan decrease, a state results in which the resistance for the auxiliary heater becomes higher and higher, and the auxiliary heater continually adjusts the heat output down. This can lead to the counterpressure which is produced by the motor vehicle heater fan being higher than the pressure of the auxiliary heater. This state is also called overpressurization. The heat of the auxiliary heater can then no longer be delivered. In the extreme case, it is transported in the opposite direction. This can lead to the fact that the overheating protection generally located in the outlet area of the auxiliary heater can be shut down. Furthermore, serious damage to the entire system can occur, for example, in the inlet area or on the control device of the auxiliary heater.